1. Field of the Invention
This invention relates to a vibration type driving apparatus in which a vibration member of which the vibration is excited and a contacting member contacting with the vibration member move relative to each other.
2. Related Background Art
An already proposed vibration-type driving apparatus is constructed as shown, for example, in FIG. 6 of the accompanying drawings. This vibration type driving apparatus has a ring-like vibration member 61 and a moving member (contacting member) 74.
The vibration member 61 is comprised of an elastic member 63, a group of piezoelectric elements 64 adhesively secured to the underside of the elastic member 63, and a friction member 66. adhesively secured to the upper surface (contacting surface) of the comb-tooth-like portion of the elastic member 63, and the underside of the moving member 74 is brought into pressure contact with the upper surface (sliding surface) of the friction member 66 by pressing means, not shown.
In the vibration type driving apparatus thus constructed, when a periodic signal is applied to the group of piezoelectric elements 64, a travelling wave in which elliptical motions having a plurality of time phase differences are combined together is excited in the surface particles of the vibration member 61 (the elastic member 63 and the friction member 66), and the moving member 74 is frictionally driven and rotated. Accordingly, the frictional contact state between the vibration member 61 and the moving member 74 is a factor which determines various kinds of performance such as the output torque, the number of revolutions, the energy efficiency and the life of the driving apparatus.
So, heretofore, polishing work (see Japanese Patent Application Laid-Open No. 2-211074) or grinding work (see Japanese Patent Application Laid-Open No. 1-286783) has been done to make the flatness and surface roughness of the sliding surface of the friction member 66 fall within a predetermined range. There is also a case where the portion around the sliding surface of the friction member 66 is worked into a predetermined shape by cutting work (see Japanese Patent Application Laid-Open No. 6-46580). In the polishing work and the grinding work, however, the handling of the friction member 66 is inconvenient and requires a long working time and a high cost. Also, in the polishing work and the grinding work, irregularity is liable to occur to the finished state of the sliding surface, and this is considered to directly affect the irregularity of the performance of the vibration type driving apparatus.
Also, the cutting work requires many steps and moreover, the work must be done individually for each member, and in addition, to finish the cut shape between workpieces uniformly, it is necessary to strictly effect the custody of a parameter such as a working force, and this is inconvenient and takes a long working time.
Further, the friction member 66 popular in the vibration type driving apparatus, as shown in FIG. 7 of the accompanying drawings (a cross-sectional view taken along the line 7xe2x80x947 of FIG. 6), is formed of a hard additive 84 and relatively soft binder resin 85 and therefore, when it is cut by a cutting tool, cutting resistance increases in the portion of the additive and decreases in the portion of binder-resin. Therefore, the cut surface becomes an uneven surface in which the additive protrudes from the binder-resin, and a suitable smooth surface is difficult to obtain.
As regards other material of the friction member, for example, in Japanese Patent Application Laid-Open No. 5-239442 and Japanese Patent Application Laid-Open No. 4-49872, a resin material containing carbon fiber is disclosed as a material being good in abrasion property and suitable as a frictional material for a vibration wave motor from the long durability life and the stability of the coefficient of friction thereof.
However, when the evaluation of the performance of the vibration wave driving apparatus under various environments has been effected in the various uses of the vibration wave driving apparatus, it has been found that the abrasion resistance of a frictional material, i.e., the abrasion loss of the frictional material, is remarkably changed by the influence: of a change particularly in humidity. Therefore, it has been found that the life of the vibration wave driving apparatus depends greatly on the durability life of the frictional material and is greatly changed under the influence of a change in the humidity particularly in the environment of use.
A frictional material for a vibration wave driving apparatus stable against the influence of a change in humidity under an environment of low humidity or high humidity or under an environment in which there are changes in humidity is desired.
One aspect of the invention is to provide a friction member on the sliding portion of at least one of a vibration member and a contacting member which are the constituent members of a vibration wave driving apparatus, and smoothly working the sliding surface of the friction member by the pressing of a mold, thereby obtaining the sliding surface which can be worked more easily and in a shorter time than by cutting in the prior art and which is free of irregularity and assumes proper flatness and proper surface roughness.
One aspect of the invention is to provide a friction member on the sliding portion of at least one of a vibration member and a contacting member which are the constituent members of a vibration wave driving apparatus, the friction member being formed of a resin composition containing heat resisting resin and carbon fiber of the mesophase pitch origin, and stable driving can be realized even under an environment of low humidity or high humidity.